1. Field of the Invention
This invention relates to thermoplastic foam processing and products.
2. Description of the Prior Art
Thermoplastic structural foams are fabricated by two main processes: injection molding and extrusion. Both processes for producing foams yield products which do not have uniform cell structure and do not have low densities. In addition, foamed parts made by the injection process have unusually long cooling times.
Various attempts have been made to reduce part weight and cycle time and to produce more uniform cell size of injection molded and extruded structural thermoplastic foam. Partially effective results have been achieved with a multiple stage modifier having a first stage polymerized from MMA and EA in a 15/10 weight percent ratio and 75 weight percent of second stage from MMA. However that material did not achieve sufficiently low densities, cycle times, and final part appearance to meet the needs of this industry.